Ivanova O. Martensitic transformation and mechanical behaviour of non-stoichiometric intermetallic compound Ti75,5Sn24,5

This work is devoted to the investigations the martensitic transformation into non-stoichiometric compound Ti3Sn with composition Ti75,5Sn24,5. We studied crystal lattice changes accompanied the transition, room temperature mechanical and effect of Zr and Al additions on the transformation in Ti75,5Sn24,5. We determined crystal lattice changes associated with this transformation using X-Ray diffraction experiments with heating in situ. The crystal structure of low-temperature was defined using XRD analysis and confirmed by electron diffraction in TEM. The as cast Ti75,5Sn24,5 was found to consist mainly of an orthorhombic Cmcm martensitic phase at room temperature; upon heating to 473 K the material undergoes a reversible group-subgroup transition to hexagonal P63/mmc (D019) phase. Orientation relations between parent and product phases and transformation strain was determined and discussed. Then mechanical properties of Ti75,5Sn24,5 were studied at room temperature. We observed a strain recovery of the material using a compressive cyclic loading-unloading test and microhardness indentation at room temperature. During loading-unloading processes forms pseudoelastic the stress-strain curve loop while irregular shape of microhardness imprints indicates graphically material's recovery. The fully recrystallized material with small grains about 20 ?m recovers about 1,2% of deformation, shows strain to failure 18%, yield stress 460 MPa and ultimate stress about 650MPa without breaking in compression. Microstructure observation of deformed material revealed that cracking in Ti75,5Sn24,5 begins in the initial stages of deformations. Cracks propagate displaying crack's bridging and leads to continuous fracture. Effect of 1at.% and 3at.% of Al and Zr on the phase transition in Ti3Sn was studied by dynamical mechanical analysis. Additions of Zr and Al leads to significant increasing of Young's modulus and to degreasing of damping capacity. The lowest Young's modulus was found in binary arc melted Ti75,5Sn24,5 composition (about 4GPa at transformation temperature) while the composition Ti75.5Sn21.5Al3 shows the highest from all studied alloy Young's modulus about (E=40 GPa). Damping capacity arc melted Ti75,5Sn24,5 with 1at.% and 3at.% of Zr and Al was found to be around 4-7% while for arc-melted Ti75,5Sn24,5 it reaches to 25%. Additions of Zr and Al lower the transformation temperature and increase the thermal hysteresys and Young's modulus and lower damping capacity